Fracture strengths of three core restorative materials supported with or with- out a prefabricated split-shank post Brett I. Cohen, PhD, a Mark K. Pagnillo, BS,b Allan S. Deutsch, DMD, c and Barry Lee Musikant, DMD d Essential Dental Systems, S. Hackensack, N.J. Purpose. The aim of this study was to compare the fracture strengths of three restorative materials, a lanthanide reinforced composite (Ti-Core Natural), a silver amalgam (Tytin), and a hybrid glass ionomer (Advance), supported by either a multitiered, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post. Material and methods. A total of 60 recently extracted single-rooted human teeth were divided into six groups of 10. All groups were stored at 100% humidity at room temperature for 1 week before testing. Each specimen was placed in a special jig at a 45-degree angle to the buccolingual axis and subjected to a load that was recorded in pounds and converted to Newtons on a universal testing machine, with a crosshead speed of 0.63 cm/minute until failure. Two-way analysis of variance followed by the Newman- Keuls pairwise multiple comparisons test were used to compare the results. Results. There was a statistically significant difference between core materials (p < 0.001 ), but not regarding post conditions. Ti-Core Natural material had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material and the latter two core materials (Tytin and Advance) do not differ from each other. There was no statistical difference between Ti-Core material supported by a post and Ti-Core material supported without a post. (J Prosthet Dent 1997;78:560-5.) Restorative materials commonly used as core materials for pulpless teeth are silver amalgam, glass ionomer, hybrid glass ionomer materials, and compos- ite. v~° Silver amalgam still represents one of the most commonly used core materials and can be used alone or in combination with a pin or post. 2,H The primary dis- advantages of silver amalgam are the long setting time and low initial compressive strength. The glass ionomer materials have some favorable characteristics, which in- clude a weak bond to enamel and dentin, fluoride re- lease, and a low coefficient of thermal expansion. 4a°'12 The disadvantages of glass ionomers are their lack of strength, brittle characteristics, and sensitivity to mois- ture.~3 ~6Hybrid glass ionomer materials develop a weak bond to enamel and dentin and can be light cured. The disadvantages of hybrid glass ionomer materials include ~Vice-President of Dental Research. bResearch Scientist/Chemist. cCo-Director of Dental Research. ~Co-Director of Dental Research. relative low compressive and diametral tensile strengths) 4-16 Hybrid glass ionomers may behave as hydrogels (hygroscopic-like materials), which absorb water and cause swelling and weakening of the mate- r i a l ) 4-16 Composites offer several advantages, such as ease of manipulation and rapid setting time when compared with dental amalgam. 13aTa8 It has been reported that a tita- nium-reinforced composite (Ti-Core, Essential Dental Systems, South Hackensack, N.J.) has a compressive and diametral tensile strength value (284 MPa [41,131 psi] and 36 MPa [5,219 psi], respectively), 13a9 which ap- proaches that of dentin (297 MPa [43,100 psi] and 41 MPa [6,000 psi], respectively). 2° Ti-Core material has also been reported to release fluoride for 1 year. 21 Post retention in a root canal is believed to be an im- portant factor for a successful restoration where little or no coronal dentin is present. The Flexi-Flange dowel (Essential Dental Systems) with its multitier system maximizes dentin-to-metal contact to distribute func- tional stresses to the strongest part of the root, the coro- 560 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 78 NUMBER 6
Transcript
Fracture strengths of three core restorative materials supported with or with- out a prefabricated split-shank post
Brett I. Cohen, PhD, a Mark K. Pagnillo, BS, b Allan S. Deutsch, DMD, c and Barry Lee Musikant, D M D d Essential Dental Systems, S. Hackensack, N.J.
Purpose . The aim of this study was to compare the fracture strengths of three restorative materials, a lanthanide reinforced composite (Ti-Core Natural), a silver amalgam (Tytin), and a hybrid glass ionomer (Advance), supported by either a multitiered, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post. Mater ia l and me thods . A total of 60 recently extracted single-rooted human teeth were divided into six groups of 10. All groups were stored at 100% humidity at room temperature for 1 week before testing. Each specimen was placed in a special jig at a 45-degree angle to the buccolingual axis and subjected to a load that was recorded in pounds and converted to Newtons on a universal testing machine, with a crosshead speed of 0.63 cm/minute until failure. Two-way analysis of variance followed by the Newman- Keuls pairwise multiple comparisons test were used to compare the results. Results . There was a statistically significant difference between core materials (p < 0.001 ), but not regarding post conditions. Ti-Core Natural material had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material and the latter two core materials (Tytin and Advance) do not differ from each other. There was no statistical difference between Ti-Core material supported by a post and Ti-Core material supported without a post. (J Prosthet Dent 1997;78:560-5.)
R e s t o r a t i v e materials commonly used as core materials for pulpless teeth are silver amalgam, glass ionomer, hybrid glass ionomer materials, and compos- ite. v~° Silver amalgam still represents one of the most commonly used core materials and can be used alone or in combination with a pin or post. 2,H The primary dis- advantages of silver amalgam are the long setting time and low initial compressive strength. The glass ionomer materials have some favorable characteristics, which in- clude a weak bond to enamel and dentin, fluoride re- lease, and a low coefficient o f thermal expansion. 4a°'12 The disadvantages of glass ionomers are their lack of strength, brittle characteristics, and sensitivity to mois- ture.~3 ~6 Hybr id glass ionomer materials develop a weak bond to enamel and dentin and can be light cured. The disadvantages of hybrid glass ionomer materials include
~Vice-President of Dental Research. bResearch Scientist/Chemist. cCo-Director of Dental Research. ~Co-Director of Dental Research.
re la t ive low c o m p r e s s i v e and d i a m e t r a l t ens i le s t rengths ) 4-16 Hybr id glass ionomers may behave as hydrogels (hygroscopic-like materials), which absorb water and cause swelling and weakening o f the mate- rial) 4-16
Composites offer several advantages, such as ease of manipulation and rapid setting time when compared with dental amalgam. 13aTa8 It has been reported that a tita- nium-reinforced composite (Ti-Core, Essential Dental Systems, South Hackensack, N.J.) has a compressive and diametral tensile strength value (284 MPa [41,131 psi] and 36 MPa [5,219 psi], respectively), 13a9 which ap- proaches that o f dentin (297 MPa [43,100 psi] and 41 MPa [6,000 psi], respectively). 2° Ti-Core material has also been reported to release fluoride for 1 year. 21
Post retention in a root canal is believed to be an im- por tant factor for a successful restoration where little or no coronal dentin is present. The Flexi-Flange dowel (Essential Dental Systems) with its multit ier system maximizes dentin-to-metal contact to distribute func- tional stresses to the strongest part o f the root, the coro-
560 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 78 NUMBER 6
COHEN ET At THE JOURNAL OF PROSTHETIC DENTISTRY
m
Fig. 1. Example of dentin spur used in preparation of core without post su )port.
hal portion2-' :s The threaded, split shank design for thc Flexi-Flange dowel offers high retention with minimal insertional and fimctional stresses. > es
The purpose of this study was to colnparc the fracture strengths of three restorativc materials (hybrid glass ionomer material, silver amalgam, and a composite) sup ported by eith,:r a multitiered, threaded split-shank post (Flcxi-Flange) or with a dcntin spur without post sup- port.
M A T E R I A L A N D M E T H O D S
The core materials used wcrc (1) Advance (Lot no. 9510202, Dcntsply, LD Caulk, Milford, Dcl. ), a hybrid glass ionomcr containing both a glass ionomcr portion (strontium ahmlinum fluorosilicatc glass) and a light curc resin (methacrylate monomer) ; (2) Tytin silvcr amalgam ( I,ot no. 41273, Kcrr, Romulus, Mich. ), which is an amalgam alloy containing silver, copper, tin, and mercury; and (3) Ti-Core Natural material (Ix)t no. 101495, Essential Dental Systcms), a lanthanidc-rcin forced resin composite (lanthanide metal fi'om rare earth metals) that releases fluoridc, el
A total o f 60 rccently extracted singlc-rootcd human tccth (maxillaw and mandibular canines), which werc stored in distilled water, were used. The specimens werc dixidcd into six groups of 10 specimens. Group 1 con sisted of Tvtin diver amalgam supported by a No. 1 Flcxi- Flangc dowcl. Group 2 consistcd of Tvtin silvcr amal- gam supported by a dentin spur without a post. Group 3 consisted of Fi Core Natural composite supported by a No. 1 Flexi Flange dowel. Group 4 consistcd of Ti- Core Natural composite supported by a dentin spur with- out a post. Group 5 consisted of Advance hybrid glass ionomer with a No. 1 Flexi-Flangc dowel. Group 6 con- sisted of Adv,-nee hybrid glass ionomcr material sup ported by adc ntin spur without a post.
For this stuJy, 30 teeth wcrc sclcctcd and had their crowns rcduc~d to the cemcntocnamcl junction (CEJ) wi th d i a m o u d i n s t r u m e n t s ( D i a t c c h d i a m o n d ,
ter of S h a f t
Fig. 2. flexi-flange No. I dowel.
Herrburgg, S\~ itzerland ), leaving a dentin spur remain- ing at one sidc (Fig. 1 ). The canals of thcsc tccth were prepared with thc fhll lcngth of a No. 1 Flcxi-Flangc primary reamer without the countersink preparation. This canal space was filled with core material x~hen the corcs wcrc Elbricatcd. The other 30 teeth had their cro\~ns removed at CEI with the same diamond stone and were endodonticallv prcparcd to recci\c a No. 1 Flexi-Flange dowel according to lnanuthcturer's instruc tions. Thc dimensions of the Flexi-Flangc No. 1 dowel includc a diameter of the shaf't of 1.40 mm and a head 4.5 rain ill height (Fig. 2). Onh' stainlcss stccI Flcxi- Flange dowels were used in this study and all posts were cemented into thc roots with zinc phosphatc ccmcnt (powder lot no. 101 041791 and liquid h~t m). I15 103091, Fleck's zinc ccmcnt, Mizzy, Cherry Hill, N.I.! , which was mixed according to manuf:acturcr's :ccom mendations (0.8 gin powder to 0.3 ml liquid I. Thc ce- ment was allowcd to set for at least 1 hour before cxccss CClllellt was relll(i\:cd.
A bonding agent was used bcforc cach core \~as fabri- catcd. Amalgambond bonding agent (lot no. 042596, Parkcll, Farmingdale, N.Y.) was used with Tvtin silvcr amalgam bccausc it was availablc. Thc Amalgambond was curcd with dentin activator f})r amalgam (batch no.
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Fig. 3. Tooth preparation with Ti-Core Natural core material and dentin spur.
Fig. 5. Silver amalgam with dentin spur specimen (without post) after failure.
Fig. 4. Tooth with Ti-Core Natural core supported by Flexi- Flange post.
Fig. 6. Ti-Core Natural material with Flexi-Flange dowel (with post) after failure.
9510202). Advance hybrid glass ionomer, All-Bond 2 bonding agent (lot no. 049266, Bisco Dental Products, Itasca, Ill.) was used for Ti-Core Natural composite. The All-Bond 2 procedure (lot no. 129031, Uni-Etch, Bisco Dental Products) incorporated the total etch technique for 10 seconds for composite restorations and post ce- mentation. The core materials were prepared in accor- dance with manufacturers' instructions. A hard copper band matrix (Moyco Industries Inc., Philadelphia, Pa.) was placed around each tooth for all groups studied. Ti- Core Natural and Advance core materials were placed with a centrix syringe. Tytin silver amalgam was placed by standard procedures, starting with a thick endodon- tic plugger (Hu-Friedy, Chicago, Ill.) in the root por- tion of the tooth, then with an amalgam plugger (Hu- Friedy). Each core preparation was standardized to a height of 4.5 mm with the use of diamond instruments (Diatech diamond), and then the prepared specimens were mounted in acrylic resin blocks (Formatray, Kerr Mfg.) (Figs. 3 and 4). All groups were stored in 100% hmniditv at room temperature for 1 week before testing was perfbrmed.
For testing, each specimen was placed in a special jig at a 45-degree angle on the buccolingual axis and sub- jected to a load that was recorded in pounds on a uni- versal testing machine (810 MTS, Material Test System Corp., Minneapolis, Minn.), at a crosshead speed of 0.63 cm/minu te , which was applied until failure occurred (Figs. 5 through 7).
Statistical analysis
The dependent variable was the load required to frac- ture. Two-way analysis of variance (ANOVA) was used to compare the mean load for each of the post condi- tions (with a Flexi-Flange dowel or with a dentin spur and no post) and core materials (Ti-Core, Tytin silver amalgam and Advance materials). A significant ANOVA result was followed by the Newman-Keuls pairwise multiple comparisons test. M1 results were considered statistically significant i fp < 0.05.
R E S U L T S
The ANOVA indicated that there was a statistically significant difference benveen cores (p < 0.001 ), but not
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regarding post condit ions (Table I). There was no intcr- action between the presence or absence o f a post and core material. Fur ther analysis with the Ncwman-Kculs multiplc comparisons procedure indicatcd that bo th Ti Core (with and wi thout a post) had a significantly larger mean load than either Tytin silver amalgam (with or wi thout a post) or Advancc matcrial (with or wi thout a post) and the latter two core materials (with or wi thout a post) were not diff;~rcnt f rom each other (Table 1I). There was no significant difference between Ti -Core material reinfbrced with a post or wi thout a post.
D I S C U S S I O N
This study addressed a worst case scenario where a crown was lost and where a core supported with or with ou t an endoclontic split-shank post could fail. All f'aib ures occurred either when the core material fi'actured or when the too th f?actured. N o post fi~ilures werc observcd in this stud}'.
In a study of" the fi'actural strength o f the Flexi-Post dowel with tk ree D~pes o f core materials (TbCore mate- rial, Tytin silver amalgam, and Ketac-Silver material) sup- por ted by a Flcxi-Post dowel, 29 it was reported that the T i - C o r c material s u p p o r t e d by a Flexi -Pos t dowel (914.7 N, 204.9 pounds) was significantly greater than Tytin silx er amalgam (696.4 N, 156.0 pounds) and Ir-,etac - Silvcr material (309.8 N, 69.4 pounds). > In this stud}; similar results were fbund because Ti Corc matcrial re- corded a statistically greater f?actural strength with a Flexi- Flange post (950.9 N [213.0 pounds]) and with a dentin spur wi thout post support (1030.4 N [230.8 pounds]) t h a n c i t h c r T v t i n si lver a m a l g a m wi th a p o s t (771.4 N [17'2.8 pounds] ) and wi thout a Flexi Flange post ( 628.6 N [ 140.8 pounds ]) and Advance material with a post (706.7 N, [158.3 pounds] ) and without a post (597.8 N [133.9 pounds]) (Table II). There was no sta tistically significant diflkrence between Ti-Core cores sup- por ted with ~l Flexi Flangc post or wi thout a post sup port.
For Tvtin silver amalgam and Advance material, thc fracture resist~'.ncc increased with thc support o f the Flexb Flange post, but this increase was no t statistically sig- nificant. In a similar study by Kahn et al., ~'~ f:atigue of, three prefhbricated threaded post systems (such as Flexi Post dowel) tested on a 4S-degree angle were studicd \~ith and witl~out a post. Thc control g roup \~ithout a pos t cxh ib i t cd stat ist ically lm~er failure t h re sho ld (p < 0.05; mean 13.9 MPa [2013 .6 psi]) than the ex perimcntal Fl,exi-Post g roup (mean 20.9 MPa [ 3024.5 psi]). Thc re,qfits of" this study arc similar to those o f I,attner et al. '~ who invcstigated the fractural s trcngth o f Ti -Core material, Tytin silver amalgam, and Ketac Silx er material supported by pins and found that Ti-Core material had a significantly h ighcr fracture s t rength (p = 0.01) than Tvtin silver amalgam and Kctac-Sil\cr material. Ti-(kn 'e matcrial 's highcr fracture rcsistancc
Fig. 7. Tytin silver amalgam with Flexi-Flange dowel (',~ ith i)o'q[ after failure.
may bc related to the physical properties oC l~vtin sil\ er amalgam that is weak under shear loading condit ions and is brittle, s2 Burgess et al. '~ tabulated mechanical propert ics o f various core materials and demonstra ted that resin-modified glass ionomcr materials arc ~ eakc~ than composi tcs in compressixc strength and diametral tensile s t reng ths ) "~ Resin-modified glass ionomers re- co rdcd compressive strengths o f 170 MPa (24 ,650 p s i to 200 MPa (2%000 psi) and diamctral tensile strengths of" 35 MPa (5,075 psi) to 40 MPa (5 ,800 psi las c o r n parcd with composites with compressive strcngths o f 281 MPa (40 ,750 psi) and diametral tensilc strengths of" 51 MPa ( 7,425 psi ).~'~ Thcsc data could cxplain the lower fracture thrcsholds of 'Advance material compared with Ti-Corc material.
Kovarik ct al. ~4 suggested that when a t'errulc is at least 2 mm below the margin of ' the core, any core ma terial is acccptable~ however, thcre arc clinical situations xxherc there is not enough remaining tooth sH'tlCttllC tot a 2 m m fcrrulc. \.\;hen this occurs, the margins ot:thc crown must be placcd at or just bclo\~ the corc and then the choice o f material bccomcs a fhctor in thc Stll\'i\ ability of" the restoration. In this study, the {'racturc strength o f a core matcrial \\'as tested with a post ()r with a dentin spur and no post. No artificial cr()\x n was placed on thc core prcparation, so that the strength o f the core material could be tcstcd \vithout increasing the level of'variables. This could bc the reason f'Ol the dit't~'r- cncc in the results betwccn this study and that o f Kovarik ct al., s~ who uscd zinc phosphatc ccmcnt to CClllcnt the crowns to thc core material.
C O N C L U S I O N S
The fiacturc strcngths o f 60 singlc-rooted human teeth \\ i th corcs of ' l ' i Corc material, Tvtin silver amalgam or Advancc material suppor ted by either a split shank post (Flcxi-Flange) or with a dcnt in spur and no post wcre measured on a univcrsal tcsting machine. AI! c<)res \\ ere
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THE JOURNAL OF PROSTHETIC DENTISTRY COHEN ET AL
Table I. Results of the ANOVA
Source DF Sum of squares Mean square F value Pr • F
Model 5 74621.2501 14924.2500 8.51 0.0001
Error 52 91244.2858 1 754.6978
Corrected total 57 165865.5359
Source DF Type I SS Mean square F value Pr • F
Core 2 65497.5814 32748.7907 18.66 0.0001
Post 1 2125.4456 2125.4456 1.21 0.2761
Core x post 2 6998.2232 3499.1116 1.99 0.1 464
Source DF Type |11 SS Mean square F value Pr • F
Core 2 66580.5866 33290.2933 18.97 0.0001
Post 1 2383.6272 2383.6272 1.36 0.2491
Core x post 2 6998.2232 3499.1116 1.99 0.1464
Table I I . Fracture strengths o f all g roups studied
Groups studied Mean (Newtons/pounds) SD SNK groupings*
Ti-Core wi thout post (group 4)
Ti-Core with post (group 3)
Tytin amalgam with post (group 1 )
Tytin amalgam wi thout post (group 2)
Advance with post (group 5)
Advance wi thout post (group 6)
1030.4/230.8 + 1 73/38.8 A
950.9/213.0 + 221.0/49.5 A
771.4/1 72.8 + 140.6/31.5 B
628.6/140.8 + 254.5/57.0 B
706.7/158.3 + 108.9/24.4 B
597.8/133.9 + 203.1/45.5 B
*Please note: Different letters indicate statistical differences among groups.
tested without the placement of artificial crowns. Un- der the conditions of this study, the following conclu- sion were drawn.
1. Ti-Core material supported by a split-shank (Flexi- Flange) post recorded statistically significantly higher fracture resistance than Tytin silver amalgam and Ad- vance material with a post.
2. Ti-Core material without a post had statistically greater fracture resistance than Tytin silver amalgam and Advance material without a post.
3. There was no statistical difference between Ti-Core material with a post and without a post.
4. There was no statistically significant difference be- tween Tytin silver amalgam and Advance material with or without a post.
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Spyridon Condos, DDS, Clinical Instructor, New York University, New York, N.Y., and M o h amed Ahmed, BDS, Dental Assistant, New York, N.Y.
New wax-up system for achieving improved adaptation Shiraishi S. Quintessence Dent Techno11997,'20:33-46.
Purpose. Dental technicians strive to improve conventional waxing techniques and properties of wax used to reduce technique inaccuracies. This study describes a scientifically based new waxing system, the Perfect Fit system, which can be used to fabricate better fitting cast restorations. System summary. A major cause of the variability of marginal adaptation of a cast restoration is the incorrect use and limits of current waxing techniques. Although no technique can universally control the precise adaptation of wax, many factors affect the adaptation: wax selection; handling of the material; and waxing environment, storage, and maintenance of the completed pattern. This article describes the physical properties of waxing materials, the problems of the softening-pressure technique for waxing crowns, and the role of a wax separator in waxing. For the conventional method of malting a wax pattern, soft wax is applied to the internal surface on which a hard carving wax is built up to complete the pattern. Because carving wax has a higher melting point than the underlying soft wax, the soft wax on the internal surface of the pattern is softened in the application process, which accelerates deformation of the carving wax during shrinkage, especially at marginal areas. To overcome this problem, the wax for the internal surface should have a high softening point with a low thermal expansion rate. When used to create a pattern by pressing, this wax should have less expansion and less stress relief, thereby exhibiting minimal warping. The wax also should have a high yield strength to prevent deformation that occurs during removal and replacement on the die.
The author describes the development of a new wax, die hardener, wax separator, and coating material that overcomes many of the problems associated with the poor adaptation of soft wax applied to the internal surface of a wax pattern. This new system eliminates the pressure technique used in conventional waxing techniques. Through a series of illustrations covering inlays, single cast restorations, and metal frameworks for fixed partial dentures, this article illustrates the supe- rior marginal adaptation of this wax and waxing system to produce well-fitting and superior mar- ginal adapted wax patterns. RP RENNER
